National Geographic interviews Kristin Poinar, assistant professor of geology, about a chunk of ice the size of lower Manhattan breaking off of the Helheim Glacier in Greenland and tumbling into the sea. The ice was estimated to be four miles wide, a mile across and half a mile thick, but this single event is not necessarily a harbinger of climate doom. “Calving happens,” Poinar told National Geographic. “Ice isn't a good building material — you could never build a skyscraper out of it because it collapses under its own weight if it's more than 90 meters tall.”